11 million years ago the Quintessons relied on their Dark Guardians to take care of any dissent. Unfortunately for them a woker robot named A3 figured how they worked and used the Coda Remote to deactivate them thus spelling the end of Quintesson reign of Cybertron. Two million years later or 9 million years ago Megatron started a war against the Autobots. At this time word of the war was mere rumors and possibly the death of Sentinel Prime was not made public at the beginning. The ordinary common Autobots were so unconcerned of a war as they placed their hopes too much on the Guardian robots keeping the peace. Over time the Guardian robots were destroyed till only one remained, Omega Supreme. Basically the Autobots made the same mistake as the Quintessons on being over dependent on these giant robots for protection, underestimating their opponents.